High dielectric constant or permittivity, “high-k,” materials have received increasing interest recently for various potential applications including high energy-density-storage capacitor, gate dielectrics, and electroactive materials. In particular, high temperature polymers (those having a melting point greater than 150° C.) with high dielectric constant and low dielectric loss are critical as embedded capacitors, which enable microelectronic-system integration to reduce size without compromising performance or, better still, with the possibility of enhanced performance in electronic systems. High-k materials suitable for some applications, such as film capacitors for power-conditioning, power electronics in hybrid electric vehicles, pulsed power, and gate dielectric field-effect transistors, must possess processability, good dielectric properties over a broad frequency range, and be thermally stable. It is conventionally believed that no single material is able to satisfy all the above-mentioned prerequisites. Therefore, recent years have witnessed an extensive exploitation of polymer-nanocomposite strategies. The overarching goal of these efforts has been to combine the best characteristics of nanofillers with polymer substrates in a synergistic fashion to improve dielectric performance of the composite materials by maximizing the dielectric constant while managing the dielectric loss to an acceptable level. From the material science standpoint, there is clearly an increasing need for high-k, nonconducting polymers (i.e., devoid of both intrinsically electronic and ionic conduction) that are processible and compatible with high-k nanoparticles.
Poly(phenylene ether)s or “PPEs” are a family of high performance thermoplastics with good high temperature properties and excellent hydrolytic stability. An important member of the PPEs family, poly(2,6-dimethyl-1,4-phenylene oxide), commonly known as PPO, is a useful material that is commercially produced on a large scale. PPO may be prepared by an oxidative coupling polymerization of 2,6-dimethylphenol as shown below:
wherein DP is a degree of polymerization.
PPEs have been considered for low-k materials for the next generation of microelectronic devices because of excellent dielectric properties. For example, the dielectric constant, εr, of PPEs ranges between 2.4 and 2.6 and tan δ ranges between 0.002 and 0.003 (at 5 GHz for PPO). PPEs also have a low moisture absorption and are highly resistive to acids and bases. On the other hand, for these thermoplastics to be attractive as high-k dielectrics in semiconductor manufacturing processes and energy-density storage applications, the εr value would need to be substantially higher (i.e., greater than 6.0) and tan δ would need to be less than 1%.
Attempts to modify PPEs to achieve the foregoing properties using conventional methods often yields undesirable cross-linking, requires a multi-step process, or both, such that conventional methods cannot be used for producing polymers having a high degree of functionality. For example, Br—PPO reacting with sodium thiomethoxide (methylthiolate) via a nucleophilic substitution reaction according to convention methods affords methylsulfido-PPO (“CH3S—PPO”). Upon subsequent oxidation by m-CPBA, CH3S—PPO may be quantitatively converted to the sulfonyl product, CH3SO2—PPO. However, under the same reaction conditions, Br—PPOs having a higher degree of Br-functionalization (greater than 25 mol %) fails to convert to the CH3S—PPO product because of extensive gel formation during the reaction. While wishing to not be bound by theory, it is believed that as an effective concentration of benzylbromide in Br—PPO is increased, the CH3S— pendant reacted faster than methylthiolate nucleophile with the nearby CH2—Br pendant, resulting in gelation of the polymerization mixture via the formation of sulfonium salt crosslinks, which is shown below:

Thus, there remains a need for polymers having suitable dielectric constants that facilitate microelectronic device manufacture and operation and improved methods for making these polymers.